Suitable duration of grazing exclusion for restoration of a degraded alpine meadow on the eastern Qinghai-Tibetan Plateau

Abstract

Grazing exclusion (GE) is a key national ecological restoration project widely applied to rehabilitate degraded grasslands. To date, there have been many debates on the effectiveness of GE for grassland recovery, and it is still poorly understood how degraded alpine meadows in the semi-humid area with relative rich rainfall in the Qinghai-Tibetan Plateau respond to GE with different durations. We selected a chronosequence of grazing-excluded alpine meadows to examine the dynamics of grassland functions. The results showed that the dominant functional group shifted from forbs to graminoids after 8 to 10 years GE and then returned to forbs. The plant population density increased significantly with GE time (P < 0.01). The total biomass, species richness, Shannon diversity index, and relative importance value of graminoids first increased and then decreased with increasing plant population density, whereas the relative importance value of forbs presented the opposite trend. All turning points were between 1350 and 1650 plants per m2 which occurred from 8 to 10 years of GE. As the duration of GE increased, the ecosystem multifunctionality first dramatically increased and then became steady after 8 to 10 years of GE. These findings imply that GE is of great practical significance to prevent degradation in semi-humid regions of the Qinghai-Tibetan Plateau, where we recommend that GE should cease after approximately 8 to 10 years to restore degraded alpine meadows from the perspective of plant productivity, diversity, community structure, and ecosystem multifunctionality.